Generally, foam, which is manufactured using various resin materials and additives, has excellent material properties. Therefore, the use thereof is rapidly expanding. Conventionally, since foam is used for simple uses, such as packaging products, external shock absorption, and the like, it has a single set of material properties because it is manufactured using a single material. However, recently, functional foam, having different material properties or colors for different parts thereof, has been increasingly required. Therefore, various methods of manufacturing such functional foam have been proposed.
Meanwhile, methods of manufacturing foam are roughly divided into a pressure method and an atmospheric method according whether or not a mold is used. In these methods, the pressure method, in which a mold is used, is a method of separately manufacturing foam corresponding to the shape of an inner molding surface of a mold by placing or charging a foaming material into the mold having the arbitrarily-shaped inner molding surface, heating and pressurizing the foaming material placed or charged in the sealed mold under suitable conditions, and then rapidly depressurizing the foaming material heated and pressurized in the sealed mold.
The pressure method is most widely used in the fields of manufacturing foam products for the reason that various foam products can be repeatedly realized according to the shape of the inner molding surface of a mold. However, basically, since the pressure method is characterized in that the external shapes of final foam products are controlled using the inner molding surface of the mold, it is extremely difficult to form a portion having specific material properties into foam products in a desired shape, so that it is impossible to realize functional foam having different material properties for different parts thereof.
In order to solve the above problem, most parties in the related field are adopting a method of manufacturing foam, in which individual intermediate foam products having different material properties or colors are first provided, and then the intermediate foam products are suitably cut and attached to form a desired shape, thereby realizing final foam products having different material properties and colors for different parts thereof. However, this method has a disadvantage in that manufacturing costs are increased because the manufacturing process thereof is complicated, and the defective fraction of products is increased because the processes of cutting and attaching the intermediate foam products are performed by hand.